Using gzip : 25.3MB/s and 8min 29 seconds for the backup to complete.
Using lzop : 373MB/s and 38 seconds for the backup to complete.

That is a 1300% increase in backup speed and in reduction in backup time.

Note:1) During these tests, gzip caused higher server load than lzop (lzop was marginally better).
2) The lzop backup was slightly larger than the gzip (300MB on a 12GB disk), but storage is cheap.
3) The /backup directory is an NFS share from our NAS server, so this also writing is across the network.

We have requested Virtualizor to add this as a backup option, it would greatly help with backing / restoring VM's where hours turn into minutes.